How to get rid of moisture around the window sill?

I have two sets of windows that are on the north side of my house. They are down low towards the ground. I just noticed that in the winter there is a lot of moisture that developes at the bottom. This has now caused mold to develope around the bottom edge of the window and window sill. How do I get rid of the mold? Also how do I stop the wondows from creating moisture during the winter, aside of rotating my house?